The invention relates generally to phase calibration systems and methods and more specifically, to phase calibration in sensor systems employed for measuring clearance.
Various types of sensor systems have been used to measure the distance between two objects. One of such sensor systems includes a capacitance probe employed to measure distance between two objects. The probe is located on one of the objects and measures a capacitance with respect to the other object for estimating the clearance between the two objects. Unfortunately, existing direct measurement techniques employing a single probe for a single target object can be relatively inaccurate where the target object changes its geometry during the course of measurement. For example, in a rotating component, such as a turbine blade, the geometry and position of the blade may change depending on various conditions. Such changes may result in a drift in the calibration of the probe.
There are several techniques that are currently used for phase calibration of the sensor systems. A commonly used technique is a “factory calibration” approach. The factory calibration is utilized to measure and control variability between parts. Some of the calibration techniques include injection of a known phase reference, and calibrating the system based on a phase to voltage conversion of a phase detector. However, phase references pose a challenge in systems that require very high accuracy such as, but not limited to, 0.1 degree. Moreover, factory calibration techniques are employed prior to installation of the sensor system and are not adapted to online phase calibration.
Another commonly used technique for calibration of a phase detector in a clearance sensor system includes subjecting a sensor to a controlled clearance change, and measuring a gain of the system as a response to the clearance change. However, this technique requires exhaustive calibration steps. Furthermore, the technique does not take into account variations that occur after the system leaves the factory.
Accordingly, there is a need for an improved method of phase calibration that addresses one or more aforementioned issues.